The present invention relates to fuel burners and methods for combusting gaseous fuels with oxidants, such as oxygen or oxygen enriched air, and in particular to such burners and methods for producing elevated temperatures in industrial melting furnaces for glass, ceramic materials, metals, etc.
Although the invention is discussed within the context of oxy/gas burners and methods of combustion for glass melting, the invention is not limited to use with glass melting or industrial melting furnaces. Persons skilled in the art will recognize that the burner and method of the present invention may be used in many other fired process heating applications.
U.S. Pat. No. 5,360,171 (Yap) discloses a burner for burning fuel in an oxidant having a fuel nozzle sandwiched between upper and lower oxidant nozzles, which are separate and distinct from one another. The burner produces fuel and oxidant jets of an outwardly divergent, fan-shaped configuration to provide a wide flame. The oxidant jets have a lower velocity than the fuel jets such that the oxidant is aspirated into the fuel. Upper and lower secondary oxidant nozzles can be provided for staged combustion.
U.S. Pat. No. 5,545,031 (Joshi, et al.) discloses a method and apparatus for discharging fuel and oxidant from a nozzle in a fashion that forms a fishtail or fan-shaped flame. In a preferred embodiment, a fuel manifold is positioned within an oxidant manifold. Both the fuel manifold and the oxidant manifold preferably have a rectangular cross section at an exit plane. In one preferred embodiment, both of the manifolds have a generally square-shaped cross section in an upstream location, which converges in a generally vertical direction and diverges in a generally horizontal direction to form the generally rectangular cross section at the exit plane. The combined converging and diverging effect produces a net momentum transfer of the fluid from a generally vertical plane to a generally horizontal plane so that the fuel and oxidant are discharged from the nozzle in a relatively wide fashion which produces the fishtail or fan-shaped flame configuration.
U.S. Pat. No. 5,611,682 (Slavejkov, et al.) discloses a staged oxy-fuel burner for producing a generally flat fuel-rich flame overlying a highly radiative fuel-lean flame. The burner has a fuel passage terminating in a nozzle, a housing surrounding the fuel passage with a space between the housing and the fuel passage, the space forming an oxidizer passage. When fuel is introduced into the fuel passage and an oxidizer is introduced into the oxidizer passage, a generally flat fuel-rich flame is produced at the nozzle end of the fuel conduit. A staging nozzle is also provided for introducing a portion of the oxidizer underneath the fuel-rich flame, which is entrained into the underside of the fuel-rich flame to produce a highly radiative fuel-lean flame.
U.S. Pat. No. 5,575,637 (Slavejkov, et al.) discloses an oxy-fuel burner similar to that in U.S. Pat. No. 5,611,682 (Slavejkov, et al.), except that this burner does not include a passage for a staging oxidizer and does not utilize staging.
U.S. Pat. No. 4,690,635 (Coppin) discloses a high-temperature burner assembly having an oxygen-containing nozzle body which has a gas conduit insert disposed therein. The gas conduit insert includes a gas conduit insert tip having a substantially flat exterior tip face with a frusto-conical shaped prominence disposed thereon and protruding from the tip face. The gas conduit insert tip includes a centrally disposed gas channel terminating at the proximal end of the frusto-conical shaped prominence to form a knife edge. An oxygen expelling orifice is concentrically disposed about the frusto-conical shaped prominence for directing oxygen therefrom to mix with the gaseous fuel for combustion within a refractory burner block.
Despite the advances made by the various designs of prior art burners, many problems still exist, including but not limited to:                reactant flow non-uniformity leading to non-uniformity in flame properties;        high levels of turbulence in the reactant streams leading to higher than desired rates of mixing and combustion;        accumulation and growth of solid carbon on the fuel nozzle tip leading to flame distortion.        
These performance related problems frequently lead to burner and process related problems, such as:                Hotter, shorter flames that result in mal-distribution of heat transfer and temperature within the process furnace. Such effects generally shorten furnace refractory life and reduce product yield.        Limitations in the percentage of oxidant that can be diverted (staged) away from the primary fuel/oxidant mixture. This limitation occurs in burners that discharge a portion of the fuel and oxidizer into a refractory burner block (sometimes referred to as a precombustor) that separates the burner assembly from the process furnace. The principal consequences of this limitation are lower rates of radiant heat transfer, lower fuel efficiency and higher NOx emissions.        Premature high-temperature failure of burner components.        Limited range of burner firing rate (fuel flow rate).        
In view of these and many other problems pertaining to prior art burners and methods for combustion, it is desired to have a burner and a method for combustion which overcome the difficulties, problems, limitations, disadvantages, and deficiencies of the prior art to provide better and more advantageous results.
It is further desired to have a more efficient burner and method of combustion for combusting a fuel with an oxidant.
It is still further desired to reduce the non-uniformity of velocities in fuel and oxidant streams at the point of initial mixing.
It is still further desired to minimize carbon buildup on fuel nozzles.
It is still further desired to achieve streamlined flow with a high degree of velocity uniformity and low turbulence levels.
It is still further desired to minimize the mean velocity differential between the fuel stream and the oxidant stream at the point of initial mixing.
It is still further desired to reduce non-uniformity in reactant flow distribution at the burner nozzle, while also reducing burner inlet gas pressure and turbulence.
It is still further desired to improve furnace performance by operating burners with higher momentum and more staging, which will lead to longer, more stable, fuel-rich flames with lower nitrogen oxide (NOx) emissions.
It is still further desired to improve furnace performance with longer, more stable flames delivering higher overall rates of heat transfer to loads in the furnace.
It is still further desired to further improve glass furnace performance by providing higher rates of heat transfer from flame to glass, thereby increasing glass bottom temperatures, enhancing recirculation of glass from refiner to tank, and reducing glass defects (increasing yield).
It is also desired to extend the range of burner firing rates.